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vp1953 Senior Member Offline Posts: 172	Placement of the SAW filter Aug 17^th, 2010, 4:58pm Hi All, Typically for ASK/FSK transceiver chips, we find that the saw filter is placed at the receiver; the other end of the SAW filter goes to the R/T switch which is connected to the antenna. Is there any issue that prevents the SAW filter from being placed between the R/T switch and the antenna (instead of at the receiver)?
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pancho_hideboo Senior Fellow Offline Posts: 1424 Real Homeless	Re: Placement of the SAW filter Reply #1 - Aug 18^th, 2010, 10:25am vp1953 wrote on Aug 17^th, 2010, 4:58pm: Is there any issue that prevents the SAW filter from being placed between the R/T switch and the antenna (instead of at the receiver)? Load stability of TX-PA. Consider impedance of SAW especially for stop band.
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vp1953 Senior Member Offline Posts: 172	Re: Placement of the SAW filter Reply #2 - Aug 18^th, 2010, 12:00pm Hi P_H, Thanks for the excellent suggestion. Is there any way this can be simulated?
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rfcooltools.com

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Re: Placement of the SAW filter
Reply #3 - Aug 18^th, 2010, 3:45pm

Adding to pancho_hideboo's comments
The saw will not see any loss between it and the antenna therefore the return loss will vary by two times the insertion loss of the switch. You could say that the impedance seen looking into the antenna from the saw filter will vary more.

Also
Tx path will now have a saw as loss so output power will be reduced by the saw insertion loss

The benefits is that fcc spurious transmission requirements will be easier to be met.

do you have an s2p file of the saw filter and switch if so check out my simulator where you can load them in and quickly try some what if scenarios for matching return loss etc.

http://rfcooltools.com

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vp1953 Senior Member Offline Posts: 172	Re: Placement of the SAW filter Reply #4 - Aug 19^th, 2010, 10:35am Hi RFcooltools, Thanks very much for your input. I will definitely play around with your simulation tool - looks pretty interesting!
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rfcooltools.com Senior Member Offline Posts: 159	Re: Placement of the SAW filter Reply #5 - Aug 20^th, 2010, 10:07am Thanks vp1953, Feel free to let me know what you think good or bad! http://rfcooltools.com
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